Free cutting alloys



Patented 26, 1939 UNITED STATES 2,184,693 I ma currnvc anno s soon Beck and um Bohnen-Bitterfeld, oemany, assignors to I. G. Farbenindustrle Aktiengesellscliaft, F'rankforton -the Main,

- Germany No Drawing. Original application November 26,

1937, 'Serial No. 178,825.

Divided and this ai plieation May 25, 1939, Serial No. 275,694. In Germany December 11,1936

1 Claim. (01. 75-146) This invention relates to aluminium base alloys and particularly to alloys of this kind'containing pmagne'sium as a major alloying component and is a divisional application from our copending 5 application Serial No. S. N. 176,625 entitled Free cuttings alloys and flied November 26, 1937.

Aluminium base alloys containing from about 3-16% of magnesium are being .widely used in various forms because of their favourable me-- chanical strength properties, their high resistance to corrosion by sea-water and alkaline agents. and also because ofthe fact'that they are readily machined by, boring, driiling, shaping, planing f or the like. When it is attempted however to utilize these favourable machining properties of the aforesaidalloys on high speed lathes'in the mass production of articles, it has been observed that the turnings formed in the operation attain an enormous length, winding round the revolving parts of the'lathes' and the workpiece itself, and

thus obstructing further proper working. 1

It is accordingly one of the objects of our, in vention'to' make aluminium magnesium alloys amenable to machining operations with high speed lathes without encountering the disadvantage hereinbefore referred to. Specifically, it is L an object of the invention to provide alloys of. g the aforesaid type which, on being machined with high-speed lathes, produceturnings which will readily break up into smaller parts, these being easily removed from the range of operation,

w while at the same time accomplishing the fore-- oing ends without disadvantageously affecting gill: physical and other useful properties of the oys. 1 A e a It has been observed that, when in aluminium alloys containing between 3 and 16% 0111188 nesiumj certain alloying components capableof forming aluminldes with the basic aluminium,

particularly manganese, vanadium, chromium, titanium, iron, nidkeland cobalt, are, present, either singly or in combination andin quantities not substantially exceedin'gabout 5%, the turnings producedinthe working of such improved alloys by high speed lathes readily break up into smaller fragments Investigation has shown that this phenomenonis caused by the presence of primary crystals of the afores'aidijahimlnides "in the crystalline texture which, being hard and s r brittle, are responsible forthe ready breaking of the alloy, do no longer formcomparatively.

seminated throughout the crystalline texture, be-

vtion ofat'least one aluminide-formin'g metal up or the turnings. On the other hand, however, it has be'nyobserved that the surface of alloys ofthe aforesaid compositions, after'being machined, regularly show a kind of pitting. Closer investigation has shown that this pitting 5 is due to the hard aluminides being present in the texture of the alloys-in the form of comparatively large crystals, -which, on working the alloys, are torn out of the machined surface by the cutting tool, ,thus yielding-a surfacewhich is not as even and smooth as desired.

The present invention is based upon-i'.he'dii scovery that by introducing also zinc intothe aforesaid alloys, the aluminides, on solidification r e crystals but are disintegrated into very. finely divided particles which, on further working the alloys by extruding, forging, etc. prior to the machining operation, easily become dising more or less uniformly distributed therein. The invention thusconte'mplates alloys of aluminium containing magnesium 'inquantities ranging between.3 and 16% and further an addiconjointly" with zinc, both the latter additions being "present in the alloy in quantities not exceeding about 5%. Preferably, the quantity of zinc incorporated in the alloy should amount 'to at least 0.2% and should not'exceed about 4%. It has further been found that -,a similar eiiect may be obtainedwhen employing aluminium magnesium alloys containin instead of. or in addition to, the aluminide-forming component, a 'certain quantity of siliconexceeding about 0.3%, which, as is known, forms a hard silicide together with magnesium. Also in this case. an addition of zinc will cause a subdivision of the hard. magnesium silicideparticles with consequential' improvement in the machining propertiesofthealloy.,fi i

The mechanical strength and other favourable properties of. the alloys hereindescribed are .not

'materially afiectedby. the addition of the. com- 2 portion of the aforesaid additions to beyond a about 3% As examples of alloys which have been found particularly useful for the aforesaid purposes,

5 the following may be mentioned:

Percent Per cent Mg 9.0 Mg 8.0 Zn 1.3 Zn 1.75 1 Fe 1.3 Fe 0.8

Mn- 0.5 $1 1.0 A1 Rest Al. Best Percent Per cent Mg 11.0 Mg 10.0 Zn 2.0 Zn 1.0 Mn 0.8 Fe 0.9 Si. 0.75 Si 0.4 20 Cr 0.4 Ti 0.3 A1 Rest Al Rest The term aluminium used herein and in the appended claim embraces the usual impurities found in aluminium ingot of commercial grade. or. picked up in the course of the usual handling operation incident to ordinary melting practice.

The alloys herein disclosed may be subjected to the usual thermal treatments familiar to those skilled in the art for the purpose of improving or altering their physical characteristics.

We claim:

An aluminium base alloy containing from about 3 to 16% of magnesium, from about 0.2 to about 4% of zinc and at least one metal capable of forming an aluminide, the total of the intentional alloying ingredients, apart from aluminium and magnesium, notexceeding about 5% of the total weight of the alloy.

ADOLF BECK. HANS BOHNER. 

